1. Field of the Invention
The invention relates to a motor-vehicle friction clutch, and more particularly to an assembly for a friction clutch having a fitting aid and transport securing means.
2. Description of the Related Art
Such a preassembled assembly has long been marketed by the applicant and is explained in more detail in the description of the figures with reference to FIGS. 3 to 5.
The preassembled assembly is supplied, for example, to the assembly line, where it is connected, for example, to the flywheel of an internal-combustion engine after the friction disc has been interposed. The weight of the pressure plate, which is only connected to the clutch casing via the tangential leaf springs, is rather high. The tangential leaf springs serve not only to connect the pressure plate to the clutch casing in a rotationally fixed manner, but also, in the installed state, to lift the pressure plate off the friction linings when disengaging the clutch, which is when the load from the diaphragm spring is relieved. The tangential leaf springs are not capable of holding the pressure plate in position during transport if they are subjected to strong vibrations in the axial direction. If the assembly is stored in the upright position before it is fitted (for example when the clutch is changed) and accidentally falls over, there is a risk of the pressure plate springing out toward the open end of the clutch casing. In the event of such axial movements, there is a risk of the tangential leaf springs being excessively extended and of no longer functioning fully when the clutch is operated. For this reason, a transport securing means is provided which prevents the pressure plate from being unintentionally deflected.
Moreover, the transport securing means serves as a fitting aid when the assembly is screwed to the flywheel. Since the diaphragm spring exerts a load on the pressure plate toward the flywheel and deflects the plate through its full axial travel, the pressure plate has to be pressed back toward the diaphragm spring when the connection screws are being tightened. Owing to the high force of the diaphragm spring, the connection screws can only be turned a few degrees into the flywheel to avoid distortion of the component during fitting or an excessive load on the screw threads.
Since the transport securing means limits the axial travel of the pressure plate, during the initiation of fitting the pressure plate does not bear against the flywheel, and since at this time there is no need to overcome any force from the diaphragm spring, it is easier to screw the assembly to the flywheel. In the known assembly, a U-shaped clip is inserted on the outside between the clutch casing and the catch part. The U-shaped clip limits the maximum possible axial travel distance (lining wear) of the pressure plate, as the transport securing means and fitting aid. This clip is clamped in place by the force of the diaphragm spring. The thickness of the clip is slightly less than the maximum permissible axial travel distance of the pressure plate. If the clutch casing is screwed to the flywheel, the pressure plate has to be pressed into the clutch casing counter to the force of the diaphragm spring toward the end of the screwing length. The catch part lifts off from the clip, and the clip falls downward or is removed outward in the radial direction by hand.
A drawback of this transport securing means is that since slight friction forces still prevail between the catch part and the clutch casing, tolerances in the thickness of the clip may lead to it not automatically falling out after the assembly has been connected to the flywheel. Deformation of the clip may also lead to it continuing to "stick" to the clutch casing after fitting, even though the catch part has been lifted off. If the assembly staff does not notice this, the clip will be flung outward by the centrifugal forces when the clutch is first used and may damage or even destroy surrounding components, such as for example the transmission unit or the like. There is also a risk of the clip not falling out completely, but rather becoming suspended somewhere in the area of the clutch. Everything will appear to be in order to the fitter who visually checks that the transport securing means has been detached. In this case too, centrifugal forces may fling the clip outward when the clutch is first used, resulting in damage.
EP 0 207 597 A1 has disclosed transport securing means and fitting aids which are provided inside the clutch casing. For this purpose, a wire spring is riveted to the casing and its free end engages in a circumferential groove which is provided in the pressure plate. In the stress-free state, the spring bears radially against the clutch casing. In order to allow the transport securing means to become active, the spring has to be pressed radially inward by means of a tool, via a hole which is provided in the casing, until it snaps into the pressure plate. At the end of the operation of connecting the preassembled friction clutch to the flywheel, the pressure plate is displaced toward the diaphragm spring in the axial direction and the spring disengages from the pressure plate and snaps back onto the inside of the clutch casing. A drawback of this design is that the pressure plate has to be additionally machined in the radial circumferential groove in order to have a defined contact surface for the spring. This additional machining is time-consuming and expensive. Moreover, it is impossible or very difficult to check the state of the spring, thus possibly preventing damage from being recognized in sufficient time. If the spring breaks, there is again a risk, as described above, of the tangential leaf springs being excessively extended, or of damage to the pressure surface of the pressure plate when the latter strikes hard against the base or the like.
The same document has disclosed further transport securing means. By way of example, a spring clip may be provided on the rivet which attaches the tangential leaf spring to the pressure plate and which, in the stress-free state, jumps back in the radially inward direction and projects axially through the clutch casing. In order to secure the pressure plate, the spring clip is pressed radially outward, and its hook-like end then positions itself against the clutch casing. This limits the axial movement of the pressure plate in the direction of the open side of the clutch casing. If the pressure plate is subjected to load in the other axial direction during fitting, the bent end of the spring clip disengages from the clutch casing and springs away in the radially inward direction, so that the transport securing means becomes free. A drawback of this design is that the spring clip may bend up in the event of excessive axial forces during transport, so that the transport securing means becomes ineffective.